1. Field of the Invention
This invention relates to a process for producing a lactone or an ester by oxidation of a ketone.
The above-mentioned lactone and ester are useful as sythetic intermediates in the production of various products including pharmaceuticals, pesticides, perfumes, liquid crystals, resins, pheromones, etc. Among them, .epsilon.-caprolactone is particularly important as a synthetic intermediate of the polyester used as a starting material of urethane polymers.
2. Related Art
A process for producing a lactone or an ester by the oxidation of a ketone using a peracid such as peracetic acid, m-chloroperbenzoic acid and the like is well known, as disclosed in Some Modern Methods of Organic Sybthesis, 3rd ed., pp. 403-407). However, the process cannot be said to be advantageous from the industrial point of view, because peracids are high in shock sensitivity and explosive.
With the aim of solving this problem, there have been developed a number of processes which comprise oxidizing a cyclic ketone in the presence of an aldehyde with various metallic catalysts (U.S. Pat. No. 3,025,306), with a soluble iron catalyst such as FeCl.sub.3, Fe(OAc).sub.3, Fe(acac).sub.3 and the like (U.S Pat. No. 3,483,222), with a soluble nickel catalyst (Japanese Patent Application KOKOKU No. 46-12456), or with soluble palladium, vanadium, molybdenum, tungsten or cerium catalyst (Japanese Patent Application KOKOKU No. 56-14095).
However, none of these processes can be said to be advantageous industrially because of low conversion and low selectivity. Apart from them, an improved process using a 1,3-diketonatonickel catalyst has been developed recently (Chem. Lett., 1991, 641). However, this process uses a homogeneous catalyst which makes troublesome the procedure for separating and recovering the catalyst from the objective product, i.e. lactone or ester, and therefore this process, too, cannot be said to be satisfactory from the industrial viewpoint.